Fluorographene and Graphane as an Excellent Platform for Enzyme Biocatalysis.

The application of enzymes is a crucial issue for current biotechnological application in pharmaceutical, as well as food and cosmetic industry. Effective platforms for enzyme immobilization are necessary for their industrial use in various biosynthesis procedures. Such platforms must provide high yield of immobilization and retain high activity at various conditions for their large-scale applications. Graphene derivatives such as hydrogenated graphene (graphane) and fluorographene can be applied for enzyme immobilization with close to 100 % yield that can result to activities of the composites significantly exceeding activity of free enzymes. The hydrophobic properties of graphene stoichiometric derivatives allowed for excellent non-covalent bonding of enzymes and their use in various organic solvents. The immobilized enzymes retain their high activities even at elevated temperatures. These findings show excellent application potential of enzyme biocatalysts immobilized on graphene stoichiometric derivatives.

Modification of Lipase with Poly(4-acryloylmorpholine) Enhances Solubility and Transesterification Activity in Anhydrous Ionic Liquids.

Tuning the molecular interaction between enzymes and their solvent environment through polymer modification can greatly improve activity and thus utility in biocatalytic reactions. In this work, this approach was exploited to enhance the activity of lipase A (LipA) from Bacillus subtilis in anhydrous ionic liquids (ILs), which are highly attractive solvents for biocatalysis. Specifically, we showed that the transesterification activity of LipA in anhydrous 1-butyl-3-methyl imidazolium hexafluorophosphate ([BMIM][PF6]) was improved up to 19-fold via covalently conjugating the enzyme with the IL-soluble polymer poly(4-acryloylmorpholine) (PAcMO). The increase in transesterification activity correlated with an increase in LipA solubility in [BMIM][PF6] as well as, notably, the number of conjugated PAcMO repeat units. Light scattering results further showed that the attachment of PAcMO disrupted the aggregation of LipA in aqueous buffer, which was used as a proxy to understand the mechanism of activation of LipA in the IL, where aggregation was more pronounced. Additionally, using static light scattering, the Flory-Huggins interaction parameter (χ) for the polymer-IL interactions was determined (0.457). The favorable PAcMO-IL interactions presumably compensated for the unfavorable interactions between the enzyme and IL, which resulted in the improvement in dissolution and, in turn, activity due to reduced diffusional limitations. Through rationally considering χ, a similar approach may be used to tune the molecular interaction between other enzymes and ILs with other polymers, which has widespread implications for the enhancement of biocatalysis in ILs.

Ultra-Small Pd(0) Nanoparticles into a Designed Semisynthetic Lipase: An Efficient and Recyclable Heterogeneous Biohybrid Catalyst for the Heck Reaction under Mild Conditions.

A novel heterogeneous enzyme-palladium (Pd) (0) nanoparticles (PdNPs) bionanohybrid has been synthesized by an efficient, green, and straightforward methodology. A designed Geobacillus thermocatenulatus lipase (GTL) variant genetically and then chemically modified by the introduction of a tailor-made cysteine-containing complementary peptide- was used as the stabilizing and reducing agent for the in situ formation of ultra-small PdNPs nanoparticles embedded on the protein structure. This bionanohybrid was an excellent catalyst in the synthesis of trans-ethyl cinnamate by Heck reaction at 65 °C. It showed the best catalytic performance in dimethylformamide (DMF) containing 10⁻25% of water as a solvent but was also able to catalyze the reaction in pure DMF or with a higher amount of water as co-solvent. The recyclability and stability were excellent, maintaining more than 90% of catalytic activity after five cycles of use.

Enzymatically crosslinked dendritic polyglycerol nanogels for encapsulation of catalytically active proteins.

The enormous potential of nanogel scaffolds for protein encapsulation has been widely recognized. However, constructing stable polymeric nanoscale networks in a facile, mild, and controllable fashion still remains a technical challenge. Here, we present a novel nanogel formation strategy using horseradish peroxidase (HRP) catalyzed crosslinking on phenolic derivatized dendritic polyglycerol (dPG) in the presence of H2O2 in an inverse miniemulsion. This "enzymatic nanogelation" approach was efficient to produce stable 200 nm dPG nanogel particles, and was performed under physiological conditions, thus making it particularly beneficial for encapsulating biological proteins. Purification of the nanogels was easy to handle and practical because there was no need for a post-quenching step. Interestingly, the use of dPG resulted in higher HRP laden nanogels than for linear polyethylene glycol (PEG) analogs, which illustrates the benefits of dendritic backbones in nanogels for protein encapsulation. In addition, the mild immobilization contributed to the enhanced thermal stability and reusability of HRP. The nanogel preparation could be easily optimized to achieve the best HRP activity. Furthermore, a second enzyme, Candida antarctica lipase B (CalB), was successfully encapsulated and optimized for activity in dPG nanogels by the same enzymatic methodology, which shows the perspective applications of such techniques for encapsulation of diverse proteins.

A three-enzyme cascade reaction through positional assembly of enzymes in a polymersome nanoreactor.

Porous polymersomes based on block copolymers of isocyanopeptides and styrene have been used to anchor enzymes at three different locations, namely, in their lumen (glucose oxidase, GOx), in their bilayer membrane (Candida antarctica lipase B, CalB) and on their surface (horseradish peroxidase, HRP). The surface coupling was achieved by click chemistry between acetylene-functionalised anchors on the surface of the polymersomes and azido functions of HRP, which were introduced by using a direct diazo transfer reaction to lysine residues of the enzyme. To determine the encapsulation and conjugation efficiency of the enzymes, they were decorated with metal-ion labels and analysed by mass spectrometry. This revealed an almost quantitative immobilisation efficiency of HRP on the surface of the polymersomes and a more than statistical incorporation efficiency for CalB in the membrane and for GOx in the aqueous compartment. The enzyme-decorated polymersomes were studied as nanoreactors in which glucose acetate was converted by CalB to glucose, which was oxidised by GOx to gluconolactone in a second step. The hydrogen peroxide produced was used by HRP to oxidise 2,2'-azinobis(3-ethylbenzothiazoline-6-sulfonic acid) (ABTS) to ABTS(.+). Kinetic analysis revealed that the reaction step catalysed by HRP is the fastest in the cascade reaction.

Synthesis and in vitro biocompatibility of injectable polyurethane foam scaffolds.

The development of therapeutics for orthopedic clinical indications exploiting minimally invasive surgical techniques has substantial benefits, especially for treatment of fragility fractures in the distal radius of osteoporotics and vertebral compression fractures. We have designed six formulations of injectable polyurethane foams to address these clinical indications. The polyurethanes were prepared by mixing two liquid components and injecting the reactive liquid mixture into a mold where it hardens in situ. Porous polyurethane foams were synthesized from lysine methyl ester diisocyanate, a poly(epsilon-caprolactone-co-glycolide) triol, a tertiary amine catalyst, anionic and non-ionic stabilizers, and a fatty acid pore opener. The rise time of the foams varied from 8-20 min. The porosity was approximately 95% and the pores varied in size from 100-1000 microm. The polyurethane foams supported attachment of viable (>95%) MG-63 cells under dynamic seeding conditions. We anticipate compelling opportunities will be available as a consequence of the favorable biological and physical properties of the injectable polyurethane foams.

A versatile library of activity-based probes for fluorescence detection and/or affinity isolation of lipolytic enzymes.

This work describes the synthesis of a library of fluorescent and/or biotinylated alkylphosphonate inhibitors being reactive towards serine hydrolases, especially lipases and esterases. Fluorescent inhibitors can be used for sensitive and rapid detection of active proteins by gel electrophoresis. Biotinylated inhibitors are applicable for the enrichment and isolation of active enzymes. Functionality as well as the different detection methods of the synthesized inhibitors were successfully tested with an enzyme preparation, namely cholesterol esterase from porcine pancreas (ppCE). Moreover, a biotinylated inhibitor was employed to enrich ppCE on avidin beads. Hence, our set of phosphonate inhibitors can be used for the detection and/or isolation of active serine hydrolases.

Modulation of lipase hydrolysis and synthesis reactions using carbohydrates.

A novel method for modulation of lipase hydrolysis and synthesis lipase was investigated by using carbohydrates in the microenvironment of the Candida rugosa enzyme. The influence of the addition of different sugars to the previously dialysed enzyme was tested on the two reactions. Rates of hydrolysis were lowered by using dialysed enzyme but were increased after sugar addition, regardless of the identity of the added sugar. In contrast, synthesis reaction rates depended on the nature of the carbohydrate. Rates were increased by adding lactose, which is not a water activity depressor, but were lowered by adding fructose, glucose, sucrose or sorbitol, which are all water activity depressors.

Enzymes from extremophiles.

The industrial application of enzymes that can withstand harsh conditions has greatly increased over the past decade. This is mainly a result of the discovery of novel enzymes from extremophilic microorganisms. Recent advances in the study of extremozymes point to the acceleration of this trend. In particular, enzymes from thermophilic organisms have found the most practical commercial use to date because of their overall inherent stability. This has also led to a greater understanding of stability factors involved in adaptation of these enzymes to their unusual environments.

Lipases for biotechnology.

Lipases constitute the most important group of biocatalysts for biotechnological applications. The high-level production of microbial lipases requires not only the efficient overexpression of the corresponding genes but also a detailed understanding of the molecular mechanisms governing their folding and secretion. The optimisation of industrially relevant lipase properties can be achieved by directed evolution. Furthermore, novel biotechnological applications have been successfully established using lipases for the synthesis of biopolymers and biodiesel, the production of enantiopure pharmaceuticals, agrochemicals, and flavour compounds.

Synthesis of a heterogeneous artificial metallolipase with chimeric catalytic activity.

A solid-phase strategy using lipase as a biomolecular scaffold to produce a large amount of Cu(2+)-metalloenzyme is proposed here. The application of this protocol on different 3D cavities of the enzyme allows creating a heterogeneous artificial metallolipase showing chimeric catalytic activity. The artificial catalyst was assessed in Diels-Alder cycloaddition reactions and cascade reactions showing excellent catalytic properties.

Creation of a synthetically useful lipase with higher than wild-type enantioselectivity and maintained catalytic activity.

[reaction: see text] We have found that two Geotrichum candidum lipase isozymes have remarkably different abilities to differentiate between enantiomers of ethyl 2-methyldecanoate. By rational recombination of selected portions of the two isozymes, we have created a novel lipase with an enantioselectivity superior to that of the best wild-type parent isozyme. Site-directed mutagenesis identified two key amino acid residues responsible for the improved enantioselectivity without compromised total activity of the reengineered enzyme.

A molecularly imprinted catalyst designed by a computational approach in catalysing a transesterification process.

A computational approach was developed to optimize the monomer formulation of molecularly imprinted catalysts. A virtual library of the intermediates of a lipase-catalysed transesterification process was constructed using Chem3D software with p-nitrophenyl acetate as substrate. The energies of the intermediates were minimized using the semi-empirical MOPAC method with the most stable intermediate expected to lead to a higher turn over rate. According to the optimization results, a MIC was prepared by co-polymerising 4(5)-vinylimidazole and itaconic acid with trimethylpropanol trimethacrylate micro spheres in the presence of p-nitrophenyl acetate. The MIC achieved of the transesterification process between p-nitrophenyl acetate and hexanol with a turn over rate of 26.2 min(-1), and showed substrate specificity towards its template with a 6.5-fold preference for p-nitrophenyl acetate over p-nitrophenyl salicylate.

Microbial lipases: production and applications.

Lipases occupy a prominent place among biocatalysts and have a wide spectrum of biotechnological applications. Lipases are unique as they hydrolyse fats into fatty acids and glycerol at the water-lipid interface and can reverse the reaction in non-aqueous media. The stability of these enzymes in organic solvents have pushed them into the frontier areas of organic synthesis leading to the designing of novel drugs, surfactants, bioactive compounds and oleochemicals. In addition, lipase-catalysed trans-esterification and inter-esterification reactions have been exploited in the fat industry. Looking into the wide scenario of lipase applications, commercialization of lipase production is a prime area of interest for microbiologists, process engineers and biochemists. Research carried out in this field has revealed that microbes, especially fungi and bacteria, are the tools of choice for commercial production. Recently, the structure determination of a few microbial lipases has widened our knowledge about the unique mechanism of catalysis of this enzyme.

Lipase mediated chiral resolution of 4-arylthio-2-butanol as an intermediate for beta-lactam antibiotics.

This paper deals with chiral enzymatic resolution of 4-arylthio-2-butanols by lipase to prepare potential intermediates of beta-lactam antibiotics. Among several lipases employed, lipase P type enzyme gave the highest ee value to prepare (R)-4-arylthio-2-butyl acetate. The enzymatic resolution of phenyl substituted alcohol (6a) using lipase P showed the highest ee value (99.7%) among those of 4-arylthio-2-butanol derivatives. Lipase P mediated hydrolysis of acylester 7a gave also (R)-alcohol 6a selectively. For determination of enantiomeric purity of these enzymatic resolved analytes, liquid chromatographic analysis was performed using two coupled Chiralcel OD and (R,R)-WhelkO chiral column.

Pilot-scale production of lipase using palm oil mill effluent as a basal medium and its immobilization by selected materials.

A pilot-scale production of lipase using palm oil mill effluent (POME) as a fermentation basal medium was carried out, and parameters for immobilization of the produced lipase were optimized. Lipase production in a 300-L bioreactor was performed using two proposed strategies, constant power per volume (P/V) and constant tip speed. Moreover, lipase immobilization on different materials was also investigated. Lipase production was performed using liquid-state bioconversion of POME as the medium and Candida cylindracea as the inoculum. The fermentation medium was composed of 1% total suspended solids (TSS) of POME, 0.5% (w/v) peptone, 0.7% (v/v) Tween-80, and 2.2% inoculum. The medium composition was decided on the basis of the medium optimization results of a previous study. The fermentation was carried out for 48 h at 30°C and pH 6. The maximum lipase production was 5.72U/mL and 21.34 U/mL, obtained from the scale-up strategies of constant tip speed and P/V, respectively. Four accessible support materials were screened for their potential use in immobilization. The most suitable support material was found to be activated carbon, with a maximum immobilization of 94%.

Chemoenzymatic synthesis of (S) and (R)-propranolol and sotalol employing one-pot lipase resolution protocol.

Synthesis of both enantiomers of biologically active propranolol and sotalol has been achieved in high optical purity by one-pot reduction of 3 and 7 followed by in situ lipase resolution of the respective chlorohydrins. Pseudomonas cepacia lipase immobilized on ceramic particles (PS-C) provided the chlorohydrin and acetate, which on nucleophilic substitution with isopropyl amine afforded the target amino alcohols in high enantioselectivity under mild reaction conditions.

Cascade synthesis of chiral block copolymers combining lipase catalyzed ring opening polymerization and atom transfer radical polymerization.

The enantioselective polymerization of methyl-substituted epsilon-caprolactones using Novozym 435 as the catalyst was investigated. All substituted monomers could be polymerized except 6-methyl-epsilon-caprolactone (6-MeCL), which failed to propagate after ring opening. Interestingly, an odd-even effect in the enantiopreference of differently substituted monomers was observed. The combination of 4-methyl-epsilon-caprolactone with Novozym 435 showed good enantioselectivity also in bulk polymerization and resulted in enantiomerically enriched P((S)-4-MeCL) (eep up to 0.88). Subsequently, a novel initiator combining a primary alcohol to initiate the ring opening polymerization and a tertiary bromide to initiate atom transfer controlled radical polymerization (ATRP) was synthesized, and showed high initiator efficiencies (> 90%) in the ring opening polymerization of 4-methyl-epsilon-caprolactone in bulk. In addition, the enantioselectivity was retained (E = 11). By using Ni(PPh3)2Br2 as the ATRP catalyst, Novozym 435 could be effectively inhibited at the desired conversion of 4-methyl-epsilon-caprolactone, thus ensuring a high enantiomeric excess in the polymer backbone. At the same time, Ni(PPh3)2Br2 catalyzed the ATRP of methyl methacrylate resulting in the formation of P((S)-4-MeCL-b-MMA) block copolymers. By this combination of two inherently different polymerization reactions, chiral P((S)-4-MeCL-b-MMA) block copolymers can be conveniently obtained in one pot without intermediate workup.

Modifying the substrate specificity of staphylococcal lipases.

The lipase from Staphylococcus hyicus (SHL) displays a high phospholipase activity whereas the homologous S. aureus lipase (SAL) is not active or hardly active on phospholipid substrates. Previously, it has been shown that elements within the region comprising residues 254-358 are essential for the recognition of phospholipids by SHL. To specifically identify the important residues, nine small clusters of SHL were individually replaced by the corresponding SAL sequence within region 254-358. For cloning convenience, a synthetic gene fragment of SHL was assembled, thereby introducing restriction sites into the SHL gene and optimizing the codon usage. All nine chimeras were well-expressed as active enzymes. Eight chimeras showed lipase and phospholipase activities within a factor of 2 comparable to WT-SHL in standard activity assays. Exchange of the polar SHL region 293-300 by the more hydrophobic SAL region resulted in a 32-fold increased k(cat)/K(m) value for lipase activity and a concomitant 68-fold decrease in k(cat)/K(m) for phospholipase activity. Both changes are due to effects on catalytic turnover as well as on substrate affinity. Subsequently, six point mutants were generated; G293N, E295F, T297P, K298F, I299V, and L300I. Residue E295 appeared to play a minor role whereas K298 was the major determinant for phospholipase activity. The mutation K298F caused a 60-fold decrease in k(cat)/K(m) on the phospholipid substrate due to changes in both k(cat) and K(m). Substitution of F298 by a lysine in SAL resulted in a 4-fold increase in phospholipase activity. Two additional hydrophobic to polar substitutions further increased the phospholipase activity 23-fold compared to WT-SAL.

Chemical modification of lipases with various hydrophobic groups improves their enantioselectivity in hydrolytic reactions.

Semi-purified lipases from Candida rugosa, Pseudomonas cepacia and Alcaligenes sp. were chemically modified with a wide range of hydrophobic groups such as benzyloxycarbonyl, p-nitrobenzyloxycarbonyl, p-methoxybenzyloxycarbonyl, t-butoxycarbonyl, lauroyl and acetyl moieties. The Candida rugosa lipase MY modified with the benzyloxycarbonyl group (modification ratio = 84%) brought about a 15-fold increase in enantioselectivity (E value) towards the hydrolysis of racemic butyl 2-(4-ethylphenoxy)propionate in an aqueous buffer solution, although the enzymatic activity was decreased. The origin of the enantioselectivity enhancement by chemical modification of the lipase is attributed to a significant deceleration in the initial reaction rate for the incorrectly binding enantiomer.